Human papillomaviruses (HPV) cause 10 000 cases of cancer of the cervix each year, as well as 3700 deaths annually. In addition, they are the cause of the most common sexually transmitted disease, genital warts, with an annual incidence of 6.2 million and a prevalence of 20 million infections (Figure 188.1). Because they produce persistent infection that in most cases is subclinical and because they are easily transmitted via intercourse, they infect more than 75% of sexually active people during their lifetime.

Of the more than 100 different DNA types of HPV, distinguished on the basis of relatedness of their genomes, 40 infect the genital area. These 40 genital types fall into two groups, distinguished on the basis of the types of disease that they produce. The first group, which includes the two most common HPV types, 6 and 11, causes exophytic condylomata, referred to as genital warts (Figure 188.2), as well as low-grade dysplasia of the vulva, vagina, and cervix. The second group, typified by types 16 and 18, causes highgrade dysplasia of the cervix, vagina, and vulva, which appears as white areas after the application of acetic acid (Figure 188.3). Lowgrade dysplasia is referred to as squamous intraepithelial lesions (SIL) grade I, moderate dysplasia as SIL grade II, and severe dysplasia as SIL grade III. Both groups of HPV viruses may produce asymptomatic infection, subclinical disease, or clinically apparent disease (Figure 188.4).